1：Experimental Design and Method Selection:

The study involved designing a PEC sensor using Pb5S2I6 crystal incorporated into polydopamine biointerface coated on nanoporous TiO2. Methods included hydrothermal synthesis, electropolymerization, anodization, and characterization techniques such as FE-SEM, XRD, UV-Vis DRS, PL, CV, EIS, and Mott-Schottky analysis. Central composite design was used for optimization.

2：Methods included hydrothermal synthesis, electropolymerization, anodization, and characterization techniques such as FE-SEM, XRD, UV-Vis DRS, PL, CV, EIS, and Mott-Schottky analysis. Central composite design was used for optimization. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: Real samples included wastewater, tomato juice, and hair color. Cr(VI) stock solutions were prepared from K2Cr2O7 in deaerated buffer.

3：List of Experimental Equipment and Materials:

Equipment included AutoLab PGSTAT, Metrohm pH meter, FE-SEM (Zeiss Sigma), XRD (Philips PW 1880), UV-Vis DRS (Shimadzu UV-2550), PL spectrofluorometer (Perkin-Elmer LS 55). Materials included K2Cr2O7, PbCl2, KI, thioacetamide, dopamine, HCl, NaOH, polyethylene glycol, NH4F, Tris buffer, acetone, ethanol, PBS, Ti foil.

4：5). Materials included K2Cr2O7, PbCl2, KI, thioacetamide, dopamine, HCl, NaOH, polyethylene glycol, NH4F, Tris buffer, acetone, ethanol, PBS, Ti foil. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Steps included preparation of nanoporous TiO2 on Ti foil by anodization, synthesis of Pb5S2I6 hydrothermally, fabrication of PEC electrode by electropolymerization of dopamine with Pb5S2I6, sample preparation for real analysis, and photocurrent measurement using chronoamperometry.

5：Data Analysis Methods:

Data were analyzed using ANOVA for CCD optimization, Randles-Sevcik equation for surface area, Laviron's theory for electron transfer, and various plots for optical and electrochemical properties.